1. Field of the Invention
The present invention relates to an image pickup apparatus, and more particularly, to automatic focus adjustment control for photographing.
2. Description of the Related Art
In recent cameras, all operations important for photographing, such as exposure determination and the focusing, are automated, and hence it is extremely less likely to cause failure in shooting by even a person unskilled in camera operations. An image stabilization system for preventing image blur caused by shaking applied to a camera has been recently studied, and hence there is almost no factors inducing a photographer's error in shooting.
However, in shooting an object under a state in which a camera is close to the object (hereinafter, referred to as macro-photographing), there has been a problem in that so-called out-of-focus shooting occurs because of a movement of the object in an optical axis direction or a movement of the camera itself in the optical axis direction caused by shaking. Therefore, in order to solve this problem, a conventional technology for correcting the out-of-focus based on an output of an acceleration sensor is disclosed in, for example, Japanese Patent Application Laid-Open No. H07-225405.
However, in the conventional technology disclosed in Japanese Patent Application Laid-Open No. H07-225405, it is necessary to mount the acceleration sensor and a processing circuit for the acceleration sensor, resulting in an increase in its manufacturing cost. In addition, spaces for mounting the devices are required, resulting in a problem in that the size of the image pickup apparatus increases.
When the acceleration sensor is not mounted, in order to suppress the out-of-focus shooting, autofocus (hereinafter, referred to as AF) for macro-photographing may be set to a so-called continuous mode. Therefore, during determination of a picture composition by a user, a distance to the object is continuously measured to adjust the focus, thereby being capable of reducing so-called defocus amount.
The continuous mode is originally provided as an AF adjustment method for a moving object. Japanese Patent Application Laid-Open No. 2001-021794 discloses that, in the continuous mode, the detecting of a defocus amount and a driving of a focus lens are continuously and alternatively performed, that an image plane position after a lapse of a predetermined time from the detection of a focus position is estimated, and that the distance to the object is continuously measured during the determination of a picture composition by the user to reduce the defocus amount.
However, during macro-photographing, a focus position frequently varies, and a focus variation speed frequently changes or a focus variation direction frequently reverses. Therefore, even when the continuos mode is set, an actual AF lens position is deviated from an object position as illustrated in FIG. 8. Thus, the defocus during macro-photographing cannot be sufficiently suppressed by the conventional AF adjustment method based on the continuous mode.